Rotordynamic Simulation Method of Induction Motors including the Effects of Unbalanced Magnetic Pull (original) (raw)

This paper presents an optimal method for rotordynamic simulation of induction motors, including the effects of unbalanced magnetic pull (UMP). The developed simulation method containing the UMP model is simple but still accurate for the actual design process of induction motors. The UMP model is simplified by using the magnetizing current without calculation of the rotor current. The effects of the slot opening and saturation are initially incorporated into the model by using the Carter factor. To improve the accuracy of the model, the magnetizing current is calculated by the finite element analysis (FEA), and the proposed correction factor is also built into the model. Moreover, mixed eccentricity is modeled and applied to the time step rotordynamic simulation for considering the actual rotor eccentricity condition. Based on the developed UMP and eccentricity models, rotordynamic simulation methods within the induction motor design process are proposed and tested in a standard four-pole induction motor. The simulation results show that inclusion of the UMP force reduces the critical speeds and generates electromagnetic excitation. The study further shows that the effects of UMP vary with a change in static eccentricity, dynamic eccentricity, slip, and bearing stiffness. Finally, based on the results, a utilization plan of the developed methods is proposed. INDEX TERMS Induction motor, mixed eccentricity, rotordynamics, unbalanced magnetic pull. NOMENCLATURE Bẟ Air-gap magnetic flux density C Damping matrix c Correction factor edy Amplitude of dynamic eccentricity emix Amplitude of mixed eccentricity est Amplitude of static eccentricity F Magnetomotive force Fg Gravity force matrix Fub Unbalance force matrix Fump UMP force matrix Fx Net UMP force in horizontal direction Fy Net UMP force in vertical direction G Gyroscopic matrix Im Magnetizing current K Stiffness matrix kC,s Carter factor for stator kC,r Carter factor for rotor kC,tot Total Carter factor Kump UMP stiffness matrix lst Stator stack length M Mass matrix N Number of turns in a winding n Degree of polynomial p Pole pair number q Displacement vector ̇ Velocity vector ̈ Acceleration vector r Air-gap radius wfν Winding factor t Time variable